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2001 M5 odd brake problem

2K views 20 replies 7 participants last post by  twalker294 
#1 ·
I had this problem crop up once several months ago but after turning the car off and back on it went away. Now however it appears to be sticking around until I get it fixed.

The other day I was driving and I felt the brake pedal gradually get stiffer until it was at the top of its travel and could barely be pushed at all. The "Brakes" and "ABS" lights then came on and by the time I got home just a few minutes later I could tell that the brakes were being applied even though I wasn't touching the pedal. Today I checked the fluid which was a bit low so I added some. I tested for a booster issue by pumping the pedal with the car off then starting it with pressure on the pedal and the pedal pushed in when the car started so it doesn't appear to be a booster problem. I then drove around the block and the pedal which started out feeling normal, quickly stiffened. By the time I got back from my trip around the block, the brakes were being applied so aggressively (without me touching the pedal,) that I had to really give it a handful of throttle to get back up my driveway and into the garage.

TL;DR - stiff pedal, brakes being applied aggressively without touching the brake pedal, booster seems OK.

Thoughts as to the cause?

Thanks
Todd
 
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#5 ·
Does turning DSC off disable ABS? In my car it does not..

I had a car exhibit the exact same symptoms and it turned out the master cylinder push rod needed to be adjusted. When the brakes are seized have you tried cracking a bleeder valve to check if the brakes are released?
 
#6 ·
Any chance something is causing the MC to overheat? Wouldn't that cause something similar?

Unhooking the electrical connection from the ABS module should take that off line to rule that out, just need to clear a code or two when done.

Regards,
Jerry
 
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#11 ·
Well disconnecting the ABS module made no difference. I rounded the block and by the time I got home the brakes were locked again and the pedal was stiff. It seems to be just the front brakes for what that's worth.

Any other thoughts?
That is what happens when you do manual bedding of brake pads. Lots of stops from about 70 or 80 down to about 30 mph. When the pedal gets hard (from heat), you know you are done. Then just ride around for a few minutes to let the brakes cool. So it still sounds like a heat issue somewhere.

If only front brakes are locking/heating up, then look at the front brakes. Have you pulled the wheels to inspect the front brakes,; pads, caliper and rotors? Any signs for overheating? Also, pull the driver side cabin filter and check your brake fluid. Anything unusual in amount, or color or smell?

Regards,
Jerry
 
#12 ·
Hmm, really odd problem. Never heard that this one comes to any E39.
try lock the vacuum line from engine to brake booster with locking pliers.
Somehow it seems that something is applying brakes, so i cant figure anything out than that you have some vacum leak or so...
My best guess would be that the part no: 9 is not working correctly. Power brake unit depression | BMW 5' E39 M5 S62 Europe

Just quessing there but we have start from something.
 
#15 ·
Unplugging the module does nothing. We learned that a year or so ago on a car with the same symptoms except back brakes were effected. Not sure why but the owner of that car said the module repair guy said that it sort of worked like light switches and unless the correct signal was sent to turn on or off some switch the switch stayed as it was. My suggestion was at the time to unplug the module and I was proven very wrong, because I dragged the owner though the diagnostics for the brakes which was a waste of time since it really was the module.

If it is only on the front you might have stuck calipers and missed all the symptoms leading up to full stuck. It could be that simple. When things are cold the pads just sit against the disc but as you drive around the block the disc heats and expands which makes the brakes start to bite harder. Not sure that explains the hard pedal. Hopefully you have looked at the booster and confirmed it is not sitting in a puddle of water.
This is a common problem. It is sort of what the video X posted but our boosters are different they are not even close to that video but a clogged drain on the compartment has the same effect because water gets drawn in to something that wants compressible air.
The first thing you need after looking for the puddle is to figure out if it is caliper or fluid/hydraulic related. The simple test for that is to pull a wheel and get a pry bar in place to force the caliper open as you would if doing a brake job. If it does not want to move then crack the bleed screw. If it then move free it is a fluid/hydraulic issue but if there is no change you simply have stuck calipers. Depending on your pads it could be easy to miss the more noticeable symptoms I suppose.
 
#21 ·
Thanks so much to everyone for their suggestions and assistance. I've determined that this issue is beyond my limited knowledge and had the car towed to the shop this afternoon. I'll be sure to come back here and post what the problem and solution was for future reference.

Again, much thanks for everyone's time and assistance.
 
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